1. Field of the Invention
This invention relates to fuel staged premixed dry low NO.sub.x gas turbine combustors of the type that are constructed with multiple concentric cylinders to which fuel manifolds are mounted. The cylinders are spaced in a staggered arrangement. Such structures of this type achieve stable combustion over a wide range of fuel-to-air ratios and low flame temperatures in the combustor resulting in low emissions of nitrogen oxides and carbon monoxide(NO.sub.x and CO, respectively).
2. Description of the Related Art
It is known, in combustor systems, that in order to reduce NO.sub.x emissions, the flame temperature in the combustor must be reduced. A well known method of reducing the flame temperature is to premix the fuel and the air prior to the mixture being combusted. However, it is also known that a premixed combustor, typically, runs over a relatively narrow operation window which is determined by lean blow-out at low fuel/air ratios and high NO.sub.x emissions at high fuel/air ratios. Flame stability is very sensitive to the fuel-to-air ratio and the fuel/air velocity. For example, if the velocity of the mixture is too high, the flame in the combustor can be blown out. But, if the velocity is too low, the combustor flame may propagate backwards into the premixing area which is commonly referred to as flashback. Also, if the fuel-to-air ratio is not properly maintained and the flame temperature gets too high, the amount of NO.sub.x created will increase which is also highly undesirable. Therefore, a more advantageous premixed low NO.sub.x combustor, then, would be presented if the combustor could be run over a larger operating window. This is particularly important with regard to the operating range of the gas turbine.
It is apparent from the above that there exists a need in the art for a premixed low NO.sub.x combustor which is efficient through simplicity of parts and uniqueness of structure, and which at least equals the NO.sub.x emissions characteristics of known premixed combustors, but which at the same time can be run over a larger operating window. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.